Centralized traffic controlling system for railroads



Aug. 9, 1938. W217, POWELL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed July 21, 1936 4 Sheets-Sheet 1 T r m nu lhll A ME 4 4 Sheets-Shet 5 .B i af Y W. T. POWELL Filed July 21, 1936 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS ,.Y Z E ME 0 R T w m E 02 34 m2 A. [u v Aug. 9,, 1938. W. TIPOWELL- 2,126,208

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed July 21, 1936 4 Sheets-Sheet 4 Lem/2m A Line fl fi INVENTOR Patented Aug. 9, 1938 OENTRALIZED TRAFFIC CONTROLL ING SYSTEM FOR RAILROAD'S Winfred '1. Powell, Rochesten N. Y., assignor to General Railway Signal'Company, Rochester,

N. Y. Application July 21,

7 Claims.

This invention relates to centralized trafi'ic controlling systems for governing traffic on railroads and it more particularly pertains to the communication part of such systems.

In a centralized traffic controlling system of the type contemplated by this invention, the switches and signals are distributed at field stations throughout the territory and are governed from the control oflice by means of the transmission of controls over a two-wire line circuit interconnecting the control ofiice with the several field stations. Indications relating to the condition of the switches and signals at the various field stations are transmitted over the same twowire line circuit to the control office.

The two line wires connecting the control office with all of the field stations in the present embodiment will be referred to as the A line and the B line. These two line wires comprise a single circuit which serves the purpose of carrying the impulses used to select the required station and for transmitting controls to the selected station, as well as serving to carry the indication messages from a transmitting station to the control ofiice for registering a calling station in the office and for transmitting indications from the registered station to the indication signal devices in the office.

The present system is of the coded duplex type, that is, it is operated through cycles of operation for the transmission of controls and/or the transmission of indications during each cycle. When controls are transmitted, a station selecting code is first applied to the line circuit for selecting the desired station and then the controls are transmitted thereto by means of additional coded impulses. When indications are transmitted, the particular field station transmitting first transmits a station registering code for registering or identifying this station in the control ofiice and then the indications from the identified station are transmitted to the control office by means of additional coded impulses.

For the transmission of controls a predetermined number of impulses of selected polarities are placed on the line circuit for operating the apparatus in the control oflice and at the field stations in synchronism through cycles of operations, irrespective of the polarity of the impulses. The distinctive polarity of the impulses of each series determines the particular station to be selected and the controls to be transmitted thereto.

For the transmission of indications a predetermined number of impulses are placed on the line circuit for operating the apparatus at the 1936, Serial 'No. 91,723

control ofiice and at the field stations in synchronism through a cycle of operations. i During a cycle for the transmission of indications alone the apparatus at all field stations and the apparatus at the controlofiice are operated, with the impulses placed on the line circuit being of a non-selecting character so that no station is selected for control during such a cycle.

During an indication cycle the apparatus at the transmitting field station functions to govern the strength of the current which is allowed to flow over the line circuit during its energization and also determines whether a change in the strength of current flowing over the line circuit is efiected or not, all for the purpose of making up the indication code.

One feature of the present invention resides in the manner in which a transmitting field station conditions the line circuit during the impulsing of this line circuit for making the impulses of comparatively weak or strong value and also for determining whether or not a weak impulse shall be changed to a strong impulse and whether or not a strong impulse shall be changed into a weak impulse during the impulsing of the line.

Another feature of the present invention resides in the manner in which the apparatus functions for the transmission of controls by means of polar impulses applied to the line circuit, in the same cycle during which this line circuit is conditioned from a transmitting field station for the transmission of indications.

Another feature of the present invention resides in the manner in which the apparatus at all field stations is initiated into operation from the control office. This is accomplished by applying a momentary impulse of alternating current to the line circuit for energizing a start relay at each station. Each start relay is connected to the line circuit in series with a condenser so that the line is normally de-energized, although the control office battery is normally connected to the line circuit for the purpose of conveniently starting a cycle of operations when a field station completes a direct current circuit for this battery.

These characteristics features of the present invention, thus briefly stated will be explained more in detail in the following description of one embodiment and one modification of the invention, while various other characteristic features, functions and advantages of a system embodying this invention will be in part pointed out and in part apparent as the description progresses.

In describing the invention in detail reference will be made to the accompanying drawings, in which those parts having similar features and functions are designated throughout the drawings by like letter reference characters which are generally made distinctive either by reason of distinctive exponents representative of their location in the system, or by reason of preceding numerals representative of their order of operation during a cycle and in which:-

Figs. 1A and 13 (with Fig. 1B placed below Fig. 1A and with correspondingly numbered lines in alignment) illustrate the apparatus and circuit arrangement employed at the control oflice for providing means whereby the operator may select the stations and govern the switches and signals throughout the territory and also for providing means whereby indications may be received from. the various field stations throughout such territory.

Fig. 2 illustrates the apparatus and circuit arrangement employed at a typical field station for providing station selection and the control of a track switch and signals at the selected station, as well as providing for the transmission of indications to the control ofiice.

Fig. 3 illustrates in schematic manner a modification of the indication receiving arrangement in the control ofiice, whereby a vacuum tube detector is provided for detecting the strength of current flowing over the line circuit in accordance with the indications transmitted from a transmitting field station.

For the purpose of simplifying the drawings and facilitating in the explanation, various parts and circuits have been shown diagrammatically and certain conventional illustrations have been employed. The drawings have been made more with the purpose of making it easy to understand the operation of the system rather than with the idea of illustrating the specific arrangement that would preferably be employed in practice. For example, the various relays and their contacts are illustrated in a conventional manner and symbols are used to indicate the connections to the terminals of batteries or other sources of current instead of showing all of the wiring connections to these terminals. Certain relays are shown in Fig. 1B in dotted line blocks to indicate that these are the same relays appearing in 1A and are connected by dotted lines.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of current and the circuits with which these symbols are used always have current flowing in the same direction, that is from to The symbols (B+) and (B-) are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of current having a mid-tap (CN) and the symbols with which these circuits are used may have current flowing in one direction or the other depending upon whether the terminal (B+) or (B) is used in combination with tap (ON).

The detailed circuit arrangement and operation of the system may be most readily understood by considering the drawings with Fig. 1B placed below Fig. 1A and with Fig. 2 placed to the right of Fig. 1A.

Control oflice equipment.The control office includes a control machine having a group of control levers for each field station. a miniature track layout corresponding to the actual track layout in the field and various indicating lamps or the like, together with apparatus and circuits to accomplish the desired functions of the system.

For example, the apparatus for one track switch is illustrated as comprising switch machine control lever SML, starting button SB, miniature track switch is and a track occupancy indicating lamp OS. A signal control lever or levers (not shown) would also be associated with the miniature track switch, but for convenience this apparatus has been omitted since the control of a track switch is considered typical of the control of other types of traffic controlling devices.

The system is started into a cycle of operations by the momentary actuation of starting button SB which stores the start condition by picking up start relay SR, which in turn picks up the corresponding code determining relay CD for determining the code to be transmitted over the line circuit during the following cycle. There is one storing relay and one code determining relay for each station in the system and they are so interlocked that, irrespective of the number of storing relays that are picked up in response to a plurality of actuations of corresponding starting buttons, only one code determining relay for a particular station can be energized during any one cycle of operations.

A neutral line relay F and a neutral line repeating relay FP are provided in the control oflice for repeating the impulses applied to the line circuit. Slow-acting repeating relays SA and SAP are provided for defining the bounds of an operating cycle, that is, these relays are picked up at the beginning of each cycle and are not dropped out until the end of each cycle.

Associated with the line and line repeating relays is a bank of stepping relays including relays IV, 2V and 3V, together with a half-step repeating relay VP. These relays are provided to mark off the successive steps of each cycle of operations.

Impulse controlling relay E serves to control the beginning and the end of each impulse period, this relay being operated in response to the step-by-step operations of the stepping relay bank. Relay E controls the operation of polarity determining relays PC and NC, which relays determine the polarity of each impulse applied to the line circuit from line battery LB at each step of the cycle, in accordance with the station selecting code and the controls to be transmitted during the operating cycle.

Message relays IM and 2M are provided to register the strength of the impulse current permitted to flow over the line circuit and to register Whether or not a change in the strength of this impulse current is effective, for the purpose of receiving indications from a transmitting field station. These message receiving relays are so conditioned at each step of the cycle. Resistance RS is provided to compensate for the resistance of the lower winding of relay IM when this relay is excluded from the line circuit under certain conditions, as will be brought out in the detailed description.

Relay CHI stores whether or not an indication is transmitted by changing the strength of current during each step and controls the executing circuit for this indication condition.

For the purpose of illustrating station registration, pilot relays IPT, 2PT. 3PT and 4PT are provided. These pilot relays are of the two-position,

' indications.

polar,;magnetic stick type although it will be understood that any suitable type relay may be employed. Indicationre'ceivingj relays IIR, 21R, 31R and AIR are also of the two-position, polar, magnetic stick type for storing the indications received from a transmitting field station, which station is registered in the control oflice by pick-- i'ng up a station'relay such asrelay ST.

A starting relay STR is provided for initiating the system from afield station at'the beginning of-a cycle of operations for the transmission of Transformer TB is for the-purpose of supplying an initiating impulse of alternating current to the line during the'start period of each cycle of operations. 7 1

Field station equipment.-The field station illustrated in Fig. 2 istypicalof all stations of the system and may be adapted for use at any location by merely connecting certain code jumpers to arrange for the desired codes, but for convenience in the description it is assumedthat this is the first station on the line by reason of the distinctive exponents employed.

A track switch TS is illustrated as being operated by a switch machine SM which is in turn controlled by switchmachine control relay SMR of the two-position, polar, magnetic stick type, governed from the control ofiice through the medium of the communication system. Suitable signals (not shown) are likewise governed through the medium of the communication system by control relays such as relay SGR The control by this relay has been omitted for the sake of simplifying the present disclosure. I

The illustrated track section is contemplated as being of the closed circuit type, with the usual track battery (not shown) and track relay T For the purpose of illustrating the transmission of a number of indications, an additional track relay T is shown in Fig. 2. Likewise, direction relays RD and LD are shown to illustrate the transmission of a number of additional indications in accordance with the present invention.

The communication part of the system includes a line relay F of the three-position, biased-toneutral, polar type, together with its quickacting repeating neutral relay FP and slowacting relays SA and SAP, all for a purpose similar to corresponding relays in the control office.

The field station includes a bank of stepping relays iV 2V 3V and the half-step relay VP arranged in a similar manner and operating in synchronism with the stepping relay bank in the control ofiice. Since the control of this bank of stepping relays is the same as the control of corresponding relays in the control oflice the detailed circuits at the field station are omitted, with the control being indicated by the dotted line Hill which connects the impulsing contact 82 of relay FP with the windings of the stepping relays.

For the purpose of illustrating station selection relay S0 is shown. This relay is picked up at the beginning of a control cycle and remains up after the transmission of the station selecting code only at the station selected for controls. Line relay F and slow-acting relay SAP of the end station are illustrated in the right hand portion of Fig. 2 to indicate how the line circuit is terminated at the station located at the end of the system.

Resistance RS is employed for the purpose of determining the strength of the impulse current Which-is permitted tofiow overthe line circuit as determined by the code provided by the transmitting field station. The inclusion or exclusion of this resistance is controlled'by pulsing relays P and 1 only at a transmitting field station. 'Chan'ge relay CH 'is provided to register a change in: any of the trafiic controlling devices at the station so that the system will be initiated for.theltransmission of indications. The operating, circuits of this change relay have been omitted but it willbe understood that it responds to a. change in position of the track relay and the-like by: meansof the momentary de-energization of its stick' circuit, in a manner which is disclosed. in Patent 1,'852,402.

"Lock-out relay LO is provided to determine when thisfield station'is to transmit its indications. Whenever thelock-out' relay is picked up during a cycle for permitting the associated field station to transmit, pulse relays P and P? are rendered effective to be governed in accordance with the code jumper positions and the positions of the various relays for applying the proper code combinationto the line circuit. Impedance 1M is connected in series with the upper winding of relay L0 and is for the purpose of preventing the flow of sufificient alternating current during the initiating period of a cycle for picking up relay L0 By the provision of impedance 1M and condenser C the initiating impulse of alternating current is kept out of the winding of relay L0 and is caused to em ergize the winding of starting relay STR The modification" illustrated in Fig. 3 makes use of the same circuits illustrated in the other figures, except that a biasing resistor BB is connected in circuit with the line battery LB for the purpose of applying a biased potential to the input-of vacuum tube VT for detecting the strength of the current which is permitted to flow over the line circuit, for operating or not operating message relay M inaccordance with indications transmitted over the line. Resistance R8 at the field station corresponds to resistance RS of Fig. 2, except that in the Fig. 3 modification thisresistance is removed from the line circuitat a transmitting field station by the picking up of pulse relay P When either a code determining relay CD or a station start relay STR. is pickedup the primary winding of transformer TF is energized for rendering the vacuum tube active.

Operation The system of the present invention is nor mally at rest and it may be initiated into a cycle of operations from the control ofiice when new controls are to be transmitted or from a field station when new indications are to be transmitted. In the event that new controls and new indications are ready to be transmitted at the same time at the beginning of a cycle, then the duplex feature of the system permits this transmission-simultaneously during the same cycle.

For convenience in describing the operation of the present system, an operating cycle will be divided into a number of impulse periods separated by time spaces and these impulse periods will be referred to as on periods of the cycle, with the time spaces between impulses being referred to as off periods of the cycle.

Normal conditions-The normally d e-energized line circuit may be energized with direct current by a transmitting field station picking up it's lock-out relay for closing up the line circuit which permits its energization from battery LB in the ofiice. Although the line is normally open to. direct current at the end station, the control office may pick up the starting relay at each field station by applying a momentary impulse of alternating current to the line, which is effective to pick up the associated starting relays.

In the control ofiice, code sending relay NC is normally energized over a circuit extending from back contact I0 of relay STR, back contact II of relay SA, through all of the back contacts of .all CD relays in the CD relay bank, including back contact I2 of the illustrated CD relay, NC bus and winding of relay NC to All other relays in the control office are illustrated as being in their normally de-energized positions.

At the field station, it is assumed that the track section with which track relay T is associated is unoccupied, therefore relay T is normally energized. Change relay CH is normally energized by means of a circuit not shown in the drawings.

Manual start-For the purpose of considering the operation of the present system for the transmission of controls, it will be assumed that the station illustrated in Fig. 2 corresponds to starting button SB illustrated in Fig. 1A and a detailed explanation will be given of the operation when button SB is actuated for selecting this station. It will be assumed that switch machine lever SML is positioned to the right for controlling the actuation of the track switch illustrated in Fig. 2 to its normal position.

The actuation of button SB closes a circuit for picking up relay SR which extends from contact of button SB and upper winding of relay SR to Relay SR closes a stick circuit for itself extending from front contact I3 and upper winding of relay SR to Assuming that no other SR relay is picked up by the operation of some other starting button, a circuit is closed for picking up relay CD which extends from back contact I4 of relay SAP, front contact.I 5 of relay SR, back contact I6 and winding of relay CD to Relay CD closes a stick circuit for itself which extends from front contact I! of relay SR, front contact I5 and winding of relay CD to It is assumed that relays SR and CD, associated with the first station in the system, are the first in the series of storing and code determining relays in the bank. The opening of back contact I5 of relay SR interrupts the series pickup circuit for the other CD relays, which circuit leads to the next SR relay contact similar to contact I5. Therefore, although some other SR relay may be picked up, the circuit for picking up its associated CD relay cannot be energized until the end of the present cycle, when relay SR will be dropped for closing back contact I5 as will be later explained.

It will thus be seen that, by means of this series pick-up circuit, only one CD relay can be picked up at any one time and that one will be the one nearest the live end of the series pick-up circuit extending to back contact I4 of relay SAP. This arrangement permits the storing of a plurality of outgoing calls and the transmission of these calls over the communication system, one at a time in an order determined by the location of the CD relays in the series.

The picking up of relay CD closes a circuit for picking up relay SA which extends from front contact I8 of relay CD, back contacts I9 and 20 of relays VP and IV respectively and winding of relay SA to The picking up of relay SA closes an obvious pick-up circuit for relay SAP at front contact 2|.

Since-relay SAP is relatively slow in picking up, during the interval between the picking up of relay SA and the picking up of relay SAP, a circuit is closed for energizing the line circuit from the source of alternating current. This circuit extends from the left hand terminal of the upper winding of transformer TF, back contact 22 of relay SAP, front contact 23 of relay SA, B line conductor, back contact I22 of relay SAP upper winding of relay STR condenser C A line conductor, front contact 24 of relay SA and back contact 25 of relay SAP to the right hand terminal of the transformer winding. This momentary application of alternating current to the line circuit is effective to pick up relay STR and since the starting relays at other stations are likewise connected across the line circuit in series with similar condensers, all of these other starting relays will be picked up.

The picking up of relay STR closes a stick circuit for itself extending from back contact I20 of relay SAP front contact I2I and lower It will be underwinding of relay STR to stood that other starting relays at the other stations close similar stick circuits for themselves.

Referring back to the control office, the picking up of relay SA closes a pick-up circuit for I relay E which extends from front contact 2| of relay SA, back contacts 26, 27, 28 and 29 of relays 3V, 2V, IV and VP respectively and winding of relay E to Before relay SA is picked up, normally energized relay NC is dropped because of open back contact I2 of relay CD. After relay E picks up a circuit is closed for picking up relay PC which extends from front contact 30 of relay E, back contacts 3|, 32 and 33 of relays 3V, 2V and IV respectively, front contact 34 of relay CD, jumper 35 in its full line position, PC bus and winding of relay PC to It will be assumed that the station illustrated in Fig. 2 responds to a station selecting code of +,on the first two steps of the cycle. Therefore the polarity of the first impulse is as determined by code jumper 35 in its full line position. This circuit arrangement for determining the polarity of each impulse will be explained in detail later.

Referring to the field station, the picking up of relay STR closes a circuit for picking up relay S0 which extends from (CN), back contact H0 of relay SA front contact III of relay STR and upper winding of relay S0 to (B).

stations are picked up over similar circuits.

The picking up of relay STR closes a circuit for picking up relay SA which extends from front contact II2 of relay STR and winding of relay SA to During the impulsing of the line circuit, relay FP intermittently closes an energizing circuit for relay SA at front contact I00 and this intermittent closure is at such a rate that relay SA does not have time to drop between impulses. As long as relay SA is picked up an energizing circuit is closed for relay SAP at front contact I03. The picking up of relay SA closes a stick circuit for relay SO which extends from (CN), front contact IIO of relay SA front contact I04 of relay S0 back contact I05 of relay FP and upper winding of relay S0 to (B). Before this stick circuit is opened at back contact I05 of relay FP during impulsing, a selecting stick circuit is completed for main- It will be understood that the SO relays at all other BIS by relay F taining relay .SO energized in accordance with the code applied to the line circuit and repeated This selecting stick circuit will'be explained later.

It will be understood that similar circuits are closed at all other stations for picking up the associated SA and SAP relays. The picking up of relay SAP at the end station completes the continuity of the line circuit for direct current at front contact 289. The picking up of the SAP relays drop the .STR. relays by reason of open back contacts suchas we of relay SAP Itwill be noted that, when alternating cur: rent is applied to the line at the beginning of the cycleas just described, the line relays at the field stations are not included in the line circuit. This is because they are normally short-circuited by circuits similar to that illustrated in Fig. 2 which includes back contact Hit of relay SAP This is to prevent the undesired operation of the line relay contacts during the application of the initiating alternating current impulse. This'alternating current impulse is terminated when relay-SAP in the control oifice picks up and opens back contacts 22- and25. The picking up of relay SAP at the end sta tion marks the beginning of the first on period, since the line is now energized by direct current over a circuit extending from the terminal of battery LB in the control office, back contacts 36, N, 33 and 39 of relays VP, lV, 2V and3V respectively, lower winding of relay IM, front contact Moi relay PC, back contactv M of relay NC, windingof relay F, front contacts 25 andM of relays SAP and SA respectively, A line conductor, winding of relay F back contacts lll'l and H38 of relays P and P respectively, winding of relay F front contact 2% of relay SAP front contact are of relay- SAP B line conductor, front contacts 23 and 22 of relays SA and SAP respectively, back contact ii? of relay NC, front contact 43 of relay PC and winding of relay 2M to the terminal of battery LB. It will be understood that the line relays at all stations connected to the system are included in the above described line circuit, so that positive current flowing over this circuit picks up relay F in the control oflice and positions the polar contacts of the station line relays to the right.

A circuit is closed for picking up relay FP which extends-from front contact Ml of relay F, front contact 45 of relay SA and winding of A circuit is --closed for picking up relay FP which extends from contact i139 of relay F in its right hand'dotted position and winding of relay FP to i Polarity selection of impulses-Whenever the system is initiated from the control oflice, the first impulse (followingthe alternating current initiatingimpulse) applied to the line circuit is determined by the position of code jumper 35 and with this jumper in its full line position the first impulse is as previously described.

In the event that code jumper 35 is inits alterhate dotted line position then relay NC is picked up during the initiating period for making the first impulse due to pole changing-contacts 48, (it, 52 and :43; It will be later described that relay VP is picked up during the first on period,

relay W is picked up during the first oil period,

third.on period, relay 3V is picked up during the 1thirdoff period and relay .VPsis dropped during the fourth on period. Furthermore, it will be later described that relay E is dropped to terminate each on.period and is picked up to terminate each .ofif period.

wJWith relay IV picked up during the first off period, a circuit is closed forpicking up relay NC which extends from front contact 36 of relay E, back contacts 3| and 32 of relays 3V and 2V ,respectively front contact 33 of relay iV, front contacted of relay CD, code jumper t! in its full lineposition, NC bus and winding of relay NC to It will be understood that the droptping 'of relay E at the endyof each on period opens the above described circuit at front contact Bil, so that the PC relay or the NC relay (whichever. is up) is dropped to (lo-energize the line circuit. .With jumper 41 in itsalternate dotted line position, thelabovedescribed circuit extends by wayof the PC bus for picking up relay PC. Istwill .be noted that the control of the PC and NC relays is efiected upon the picking up of the stepping relay during the .off period, so that the next on: period is started by the picking up of relay E in response to a stepping relay operation. :Thedetailed circuit for controlling relay E will be described later.

After thefirst two impulsesare applied to the linecircuit in accordance with the positions of jumpers 35 and 41, relay PC is picked up over a circuit extending from frontcontact 30 of relay-E, backcontact 3| of relay 3V, front contact 32x of relayZV, front contact 43 of relay CD,'lever SML in its right hand position, PC bus and winding of relay PC to This determines that the third impulse will be in accordance with lever-SML in its normal position. InJthe event that lever SML is in its reverse dotted line position, then relay NC is picked up for making the third impulse M This operation occurs on each step of the cycle, that-is, during the first part 'of each cycle of "operations the code buses determine the code applied to the line for selecting the desired-station and during the latter part of the operating cycle the code buses are energized in accordance with the posit-ions of the control levers for transmittingtlie proper controls to the selected station. It has been explained how the PC and NC .relays-are selectively energized in accordance with the position of lever SML. In a similar manner front contact 3| of relay 3V extends 'through front contact iil of relay CD for selecmay ne'rgizingthe PC and NC relays in accordance with a-signal control lever or the like.

From the above it will be seen that the impulses applied to the line circuit always begin with a short application of alternatingcurrent at the start of a control'cycle, while the following impulses are of positive or negative direct current depending uponthe 'code jumpers andcontrol "levers rendered effective by the particular code determin ing re'lay which is picked up for that particular cycle. f lm'pulsing and stepping relay operations.Irrespective of thepolaritywith which the line circuit isenergized, the line relays energize the line repeating relays each time the line circuit is energized. At the beginning of the first on period a circuit isclosed for picking up relay VP in the control office which extends from front contact .5il'of relay SA, front contact of relay FP, back contact 520i relay IV and winding of relay 'VPxto The picking up .of relay VP closes a first stick circuit for itself extending from front contact 5.0 of relay SA, front contact 53 of winding of relay IV to relay VP, back contact 52 of relay IV and winding of relay VP to When relay FF is dropped during the first off period, a circuit is closed for picking up relay IV which extends from front contact 54 of relay SA, back contact 55 of relay FP, front contact 56 of relay VP, back contact 51 of relay 2V and Relay IV closes a stick circuit for itself which extends from front contact 54 of relay SA, front contact 58 and winding of relay IV to It will be pointed out at this time that relays 2V and 3V close similar stick circuits for themselves when they are picked up at front contacts 59 and 60.

When relay FF is dropped during the first off period, a second stick circuit is closed for relay VP which extends from front contact 50 of relay SA, back contact 5I of relay FP, front contact BI and winding of relay VP to When relay FP is picked up during the second on period relay VP is dropped because its first stick circuit is open at back contact 52 of relay IV and its second stick circuit is open at back contact SI of relay FP.

Relay 2V is picked up during the second off period over a circuit extending from front contact 54 of relay SA, back contact 55 of relay FP, back contact 56 of relay VP, back contact 62 of relay 3V, front contact 63 of relay IV and winding of relay 2V to The picking up of relay FP during the third on period closes a circuit for picking up relay VP which extends from front contact 50 of relay SA, front contact 5| of relay FP, back contact 64 of relay 3V, front contact 65 of relay 2V and winding of relay VP to Relay VP establishes its first stick circuit, which is the same as previously described except that it now extends through back contact 64 and front contact 65.

When relay FP drops during the third off period the above described second stick circuit for relay VP is completed and a pick-up circuit for 3V is established which extends from front contact 54 of relay SA, back contact 55 of relay FP, front contact 56 of relay VP, front contact 51 of relay 2V and winding of relay 3V to The picking up of relay FP during the fourth on period de-energizes relay VP because its first stick circuit is open at back contact 64 of relay 3V and its second stick circuit is open at back contact 5| of relay FP.

Since the fourth impulse is the last one of the cycle the next de-energization of the line is effective to return the. system to normal. This is'because when relays E and PC (or NC) are dropped to de-energize the line at the end of the fourth on period there is no other stepping relay to be picked up for changing the circuit condition for again picking up relay E. This effects the deenergization of relay SA because front contact 66 of relay FP is maintained open for a sufficiently long interval of time to allow relay SA to drop. It will be noted that the energization of relay SA is dependent on front contact 66 after relay VP picks up and opens'its back contact I9. The dropping of relay SA de-energizes the stick circuits for the half-step and stepping relays at open front contacts 50 and 54.

It will be understood that this circuit arrangement may be extended for as many steps as desired, with stepping relays being picked up during the off periods and the VP relay being shifted during the on periods. Since the operation of the stepping relays at the field stations is the same as described in connection with the control office, a description of this function will be omitted. It will be noted in Fig. 2, that contacts H3 and I62 of'r'elays SA and FP respectively are shown leading to dotted line IOI which indicates the control of the stepping relay bank.

The picking up of relay VP during the first on period deenergizes the above described circuit for relay E at back contact 29, which allows relay E to drop and by deenergizing the selected PC or NC relay the first "on period is terminated, after which relay IV is picked up.

The picking up of relay IV during the first off period closes a circuit for picking up relay E which extends from front contact 2| of relay SA, back contacts 26 and 21 of relays 3V and 2V respectively, front contact 28 of relay IV, front contact 29 of relay VP and winding of relay E, to

When relay VP drops during the second on period, relay E is deenergized because of open front contact 29.

When relay 2V picks up during the second "off period, relay Eis again energized over the above described circuit which now extends through front contact 21 of relay 2V and back contact 29 of relay VP.

The picking up of relay VP during the third on period opens the energizing circuit for relay E at back contact 29 and relay E is dropped to terminate the third on period.

When relay 3V is picked up during the third off period, the above described circuit for picking up relay E is completed, but which now extends through front contact 26 of relay 3V and front contact 29 of relay VP- When relay VP drops during the fourth on period, relay E is de-energized because of open front contact 29 and, as above described, since there is no other stepping relay to be picked up relay E remains down to terminate the cycle.

It will be noted that stick circuits are provided for relays PC and NC including their front contacts 61 and 68. These stick circuits are for the purpose of sticking the selected PC or NC relay until relay E drops to mark the end of the fourth on period. Since the pick-up circuits for the PC and NC relays include front contacts of the CD relay and since the CD relay is dropped out during the fourth on period, these stick circuits prevent the premature de-energization of the line circuit by the dropping out or the CD relays.

'During the fourth on period, relay SR is de-energized when relay VP is dropped, by means of a circuit which extends from front contact I8 of relay CD, back contact I9 of relay VP, front contact 29 of relay IV, front contact I0 of relay 3V, front contact 69 of relay CD, front contact II and lower winding of relay SR to Since the energization of the lower winding of relay SR is in opposition to that of its upper winding, this relay will be kicked down. The dropping of relay SR and the consequent opening of its front contact I! de-energizes the above described stick circuit for relay CD which allows this relay to release.

Station selection for contr0Zs.When controls are to be transmitted the field stations are selected one at a time in accordance with the combination of and impulses applied to the line circuit during the first or station selection part ofthe cycle. As above pointed out, each impulse applied to the line circuit causes the step-bystep mechanism at the control office and at each field station to take one step irrespective of the as esses polarity of the impulsen Since the polarity of each impulse may be either or two steps of the stepping mechanism provide for the transmission of four different code combinations, three steps provide for eight different icode combinations and each additional step doubles the number of possible distinctive codes provided. In the present embodiment it is assumed that the number of stations is such that they may be selected on two steps of the cycle.

The circuits for the field stations are'similar, the only difference being in the positions of -the station code jumpers illustrated -in the upper portion of Fig. 2, which jumpers serve to condi-' tion or energize one or the other of two station selection buses, indicated bus and bus, in accordance with the codecall assigned to that particular station. The transmission of a code call connects a selecting stick circuit of the station selecting relay (SQ) to one or the other of those station selecting codebuses. If the code call transmitted corresponds to the code call assigned to the station, then the selecting stick circuit will be connected to an energized bus for each step. If the transmitted code calldoes not correspond to the station code call, then this selecting stick circuit will be connected to a deenergized bus at one step thereby causing the corresponding station selecting relay to be deenergized. The station with which communication is established is the one at which the station selecting relay remains energized, allother stations except this one being dropped out during the station selecting part of the cycle.

More specifically, considering the operation of Fig. 2, the first impulse applied to the line circuit was as previously described, which is effective to close the selecting stick circuit forrelay S0 during the first on period over a circuit extending from (CN), front contact N9 of relay SA front contact m4 of relay S0 back contacts H4, H5 and H6 of relays'3V 2V and W respectively, code jumper H1 in its full line position, bus, contact H8 of relay F in its rigl'it hand dotted position and upper winding of relay S0 to (B-). It will be observed that back contact W5 of relay FP isopen at this time, so that closed its front contact III at the beginning of the cycle.

During the first off period, relay F restores its contacts to their neutral positions and a stick circuit is closed for relay S0 which extends from (CN), front contact Ill! of relay 8A front con tact Hi l of relay S0 make-before-break contact MB of relay F and upper winding of relay S0 When relay FP drops, the closure of back contact m5 shunts the above described circuit through contact H8; The purposeof contact l i8 is to make up this stickcircuit before the selecting stick circuit is broken at the time relay F is dropped out. The purpose of contact m5 is to maintain this stick circuit complete after relay F is picked up during an on period until the selecting stick circuit is established. 1

During the second on period, the selecting stick circuit for relay S0 is closed and extends from (CN), front contact H0 of relay SA front contact I04 of relay S0 back contacts H t and N5 of relays 3V and 2V respectively, front contact N6 of relay lV code jumper I Hi in its full line position bus contact l ill of relay F in its left hand dotted position (because the second impulse =is as previously described) and upper Winding of relay so to (B It will thus be seen that the selecting stick circuit for relay S0 is energized or de-energized during each on period, depending upon whether the polarity ofthe received impulse connects this selecting stick circuit to the particular or bus which is-energized'in accordance with the code jumper connections. During each oil period following an on period during which the selecting stick circuit is energized, relay S0 is maintained energized over the stick circuit including contact N8 of relay F in itsneutral position and in multiple with back contact Hi5 of relay FP 1 "One-'halfof the stations have their code jumpers corresponding to jumper HT connected in an activeposition while the other half have these code jumpers connected in inactive positions.. Thus with the first impulse half of the stations will be selected by maintaining the SO relays energized at these stations, while if the first impulse is the other half of the stations will. be selected by maintaining the SO relays at these stations energized. This selection continues throughout the station selection steps for as many steps required, until the station selecting relay is energized at only one station, which isthe station that-will receive the control impulses. i

The transmission of indications and the registration of a station in the control office during a cyclewhen no controls are transmitted,'which will be later described,is effective to transmit a combination of all impulses from the control office for operating the stepping relay banks at the variousstations in synchronism with the stepping relay'bank in the control oflice. This combination of impulses is due to the fact thatno'CD relay in'the office is picked up and the circuit throughthe back contacts of all (JD-relays, including back contact" I2, is extended to relay NC at each step of the cycle for providing a impulse. This corresponds to aphantonicontrol code which is not assigned to any station, so that the transmission of such a code is'not effective -to=select a station for the transmission of controls when the system is operating through acycle for the transmission of indications alonev This of course means that one combination out of the possible number of codes cannot be used for station selection, therefore-withthe provision of two steps, although four separate cod-e combinations are available only three are used for station selection.

Transmission of controls.Assuming that the proper code combination is applied to the line circuit for selecting the station illustrated in Fig. ;2 the'n upon the application of the" third I impulse *to the line circuit the switch machine control relay SMR is energized from (B+) or (-B-) dependingupon thecharacter of the impulseapjplied to the line circuit. With lever SMLv in its right hand position a impulse is ar'aplied to the line circuit and a circuit is closed for energizing relay SMR in such a direction that its polar contact will be actuated to the rightfwhich circuit extends from ('CN), front contact llll of relay SAL front contact I04 of relay S0 back contact [M of relay 3V front contact I l5-of relay 2V winding of relay SMR front-contact l23- of relay S0 and contact I24 ofreiay F in itsrighthand dotted position to (B).- In the event that lever SML is in its left hand dotted position, then a impulse V is applied to the line circuit, which positions contact I24 to the left' for reversing the current flow through the winding of relay SMR, which is effective to position its polar contact to the left. Polar contact I25 of relay SMR thus assumes a position corresponding to the contact of lever SML for actuating the switch machine to normal or reverse positions over local circuits which are not shown but which are obvious.

In a similar manner .any number of additional steps may be provided for transmitting additional controls to the selected field station for governing signals and such other devices as may be employed.

When relay 2V is picked up during the second off period, the station selection operation has been completed and therefore a permanent stick circuit is closed for maintaining relay S0 energized throughout the remainder of the cycle, which extends from front contact I26 of relay 2V front contact I21 and lower winding of relay S0 to It has already been explained how the relays in the control office are deenergized at the end of the cycle and also most of the relaysat the illustrated field station. Relay S0 is deenergized at the end of the cycle when relay 2V drops and opens its front contact I26 and as previously described relay 2V is ,deenergized by the release of relay SA Transmission of indications.-Although the system is of the coded duplex type arranged for the transmission of indications from any station to the control ofiice during the same cycle that controls are transmitted to the same station or to some other station, it will first be explained how the system operates for the transmission of indications alone on a separate operating cycle. The duplex feature of "the system will be explained later in the description. Likewise, the arrangement for allowing the field stations to transmit only one at atime in a predetermined sequence, in the event that there are indications ready for transmission from a plurality of stations at the same time, will be explained in connection with the look-out feature. It will now be assumed that the station illustrated in Fig. 2 is the only one having new indications ready for transmission.

Automatic start-A change in the condition of the illustrated track section or a change in the condition of other traffic controlling devices at the illustrated station may occur for de energizing normally energized change relay CH The dropping of relay CH closes a circuit for energizing the line with direct current, which circuit may be traced from the terminal of battery LB (control office) back contacts 36, 31, 38 and 39 of relays VP, IV, 2V and 3V respectively, lower winding of relay IM, back contact 40 of relay PC, front contact 42 of relay NC, back contact 23 of relay SA, B line conductor, back contact I22 of relay SAP impedance IM upper winding of relay L0 back contact I28 of relay CH back contact I29 of relay SA A line conductor. back contact 24 of relay SA, winding of relay F, front contact 4| of relay NC, back contact of relay PC and winding of relay 2M to the terminal of battery LB. The energization of the line circuit effects the picking up of relays F, IM and 2M in the control office and relay LO at the field station. The picking up of relays IM and 2M are ineffective at this time but the picking up of relay F closes a circuit for picking up relay STR which extends from front contact 44 of relay F, back contact 45 of relay SA and upper winding of relay STR to Relay S'I'R closes an obvious stick circuit for itself at its front contact 12.

Relay NC is de-energized because of open back contact II) of relay STR and relay SA is picked up over a circuit extending from front contact II] of relay STR, back contacts I9 and 20 of relays VP and IV respectively and winding of relay SA to Relay SA effects the picking up of relay SAP and these slowacting relays are maintained in their picked up positions by means of the previously described circuits until the end of the cycle. Relay E and the stepping relays function as described in connection with a control cycle for transmitting impulses over the line circuit and for sequentially operating the stepping relay banks. All impulses are because relay NC is energized to mark the beginning of each on period by means of the previously described circuit including front contacts 30 and II of relays E and SA respectively and back contact I2 of relay CD.

During the interval between the picking up of relay SA and the picking up of relay SAP, the impulse of alternating current is applied to the line as before, which is effective to pick up the STR relays at the field stations, after which the SA and SAP relays are picked up as previously described. The system now steps through an operating cycle as before and relay L0 is stuck up over a circuit extending from front contact I30 of relay SA front contact I3I of relay SAP front contact I32 and lower winding of relay L0 to The stick circuit for relay L0 is effective as soon as this relay is picked up because back contacts I30 and I3I are then closed and during the interval between the picking up of relay SA and SAP the look-out feature is effective which will be later described.

Impedance IM connected in series with the upper winding of relay L0 is of such a resistance value that it does not interfere with the proper operation of relay LO by direct current applied to the line circuit, but this impedance unit has such an impedance value that the alternating current applied to the line circuit for picking up the starting relays is not effectively shunted by means of the bridge .across the line which includes this impedance unit. In other words IM is of low resistance and high impedance. This impedance also serves the purpose of preventing sufiicient current from the alternating current source from flowing through the upper winding of relay L0 to kick this relay down.

Registration of a field station.-At the particular station (assumed to be the station illustrated in Fig. 2) having indications to transmit, lock out relay LO is maintained energized throughout the cycle as previously explained. Recalling that the stepping relay bank in the control ofiice operates in synchronism with the stepping relay banks at the field stations, it will be noted that the closure of front contacts I33 and I34 of relay L0 applies potential to relays P and P so that'these relays will be energized or not in accordance with the condition of the channels selected by the stepping relay bank. Since no contacts similar to I33 and I34 at any other station are closed, the operation of the stepping relay banks at the other stations is ineffective to condition the as-" sociated P and P relays.

Relays IM and 2M of Fig. 1A are of the mar- .ginal type, being so designed and adjusted that they will pick up in response to a high current flow over the line circuit, but will not be picked .up and will be dropped if picked up in response to a low current flow over the line circuit. As Will be pointed out in the following description, resistance RS is inserted in the line in place of the lower winding of relay IM when the step is taken in the office. of permitting relay IM to be dropped out when picked up in response to one code transmission in readiness to be picked up or not in response to the next code transmission. Resistance RS has a resistance value approximately the same as the lower winding of relay IM in order to maintain the value of current flow over the line the same whenthe winding of relay IM is excluded from the line as when this winding is included in the line. For convenience in describing the transmission of indications the indication channels at the field station are divided into two groups, the first group being the strength of the on indications, having channels I 2 3 and 4 selected in this group. The associated strength of on indications group illustrated in Fig. 1B comprises four corresponding indication channels numbered I, 2, 3 and 4. The second group of indications at the field station comprises channels 5 I5 I and 8 which are the change of on indications. The associated indication channels in Fig. 1B at the control ofiice are the change of on? indication channels 5, 6, I and B.

,In accordance with the code jumper connections and the positions of the relay contacts in Fig. 2, the indications transmitted are as follows:No. I, high current. No. 5, no change in high current. No. 2, high current. No. 6, a change in the high current. No. 3, low current. 'No. I, no change in the low current. No. 4, low current. No. 8. a change in the low current. The above eight indications are transmitted during the four on periods of the cycle, with indications I, 2, 3 and 4 being the strength of the current during the corresponding four on periods of the cycle and indications 5, 6, I and 8 being the change or no change in the current flowing during the corresponding four on periods of the cycle.

No. I indicationis h gh-current and No. 5 is no change in current. When relay L is picked up a circuit is closed for picking up relay P which extends from code jumper I 35 in its full line position, back contacts I33, I3I, I38 and I 39 of relays IV 2V 3V and VP respectively, winding of relay P and front contact I33 of ,relay L0 to Relay P is picked up at the same time over a circuit extending from back contacts I43, I4I, I42 and I43 of relays IV 2V 3V and VP respectively, winding of relay P and front contact I34 of relay L0 to With relays P and P picked up, resistance RS is short-circuited by front contacts I01 and I88 so that the line is energized with a high value of current when relay SAP is picked up in the control office, after the Thiseffects the picking up of relays IM and This is for the purpose 2M since they are included in the energizing circuit of the line conductor.

When relayVP switches its contact I39 from a back to a front point during the first on period, the pick-up circuit of relay P is disconnected with No. I channel circuit and prepared for the No. 2 channel circuit. Since the No. 2 channel circuit may or may not be connected to and since the No. indication is no change in current, it is necessary to maintain relays P and P energized over circuits not including the No. 2 channelconductor. Relay P is maintained energized over a stick circuit which extends from back contacts I44, I45 and I46 of relays 3V 2V and IV respectively, front contact I4I of relay VP front contact I48 of relay P front contact I49 of relay P winding of relay P and front contact I33 of relay L0 to Relay P is maintained in its picked up position when relay VP picks up because the No. 5 channel conductor is'connected to(+) in accordance with the No.3 indication being no change. This circuit extends from jumper I50 in its full line position, back contacts I5I, I52 and I53 of relays IV 2V and 3V respectively, front 'con tact I43 of relay VP winding of relay P and front contact I34 of relay L0 to Referring to the control office, the No. I and No. 5 indications are conditioned during the first on period. The No. I indication, which is a high current flow over the line circuit resulting in the picking up of relay IM, is executed when relay VP picks up during the first on period by closing a circuit which extends from (B+), front contact I3 of relay IM, front contact I4 of relay E, front contact I5 of relay VP, back contact I6 of relay IV and winding of relay IPT to (CN). This positions the polar contact of relay IPT to the right. The execution of the No. I indication is terminated during the first on period when relay E drops and opens the above described circuit at its front contact I4.

Since the No. 5 indication is a no change in current value, as above described, the picking up of relay VP maintains relay 2M in the line circuit because the line circuit is now energized over a circuit which extends from the terminal of battery LB, front contact 36 of relay VP, back contact II of relay IV, back contact I8 of relay 2V, back contact IQ of relay 3V, resistance RS and over the remainder of the previously described line circuit to the terminal of battery LB. Relay 2M is maintained picked up during the first on period because the current value.

over the line circuit is maintained high and does not change.

Relay. IMis stuck up after relay VP picks up by means of a circuit extending from back contact 80 ofrelay IV, front contact 8I of relay VP, upper winding of relay IM, front contact 82 of relay IM and front contact 83 of relay E to When relay E drops to mark the end of the first on period, this stick circuit is opened at front contact 83 which effects the release of relay- IM, but since front contact I4 of relay E is opened at the same time, the shifting of contact 13 of relay IM does not result in the reverse energization of the selected channel circuit.

Relay CHI of Fig. 1B is picked up at the start of the cycle, in response to the picking up of relay SAP, over a circuit which extends from front contact 84 of relay SAP, back contacts 85, 36, 81 and 83 of relays VP, IV, 2V and 3V respectively and winding of relay CHI to Relay CHI is stuck up over a circuit extending from front contact 84 of relay SAP, contact 90 of relay 2M in either position, front contact 89 and winding of relayCHI to Since relay 2M is picked up before relay VP is picked up in the first on period and since relay 2M does not drop before the termination of this on period, relay CHI is maintained stuck up. The No. 5 indication is executed, when relay E drops to mark the end of the first on period, by closing a circuit which extends from (B+), front contact ill of relay CHI, front contact 92 of relay FP, back contact 93 of relay E, back contacts 94,

, 95 and 96 of relays 3V, 2V and IV respectively and winding of relay 2PT to (ON). This executing circuit positions the polar contact of relay 2PT to the right. The execution of the No. 5 indication is terminated during the first off period when relay FP drops and opens the above described circuit at front contact 92.

High current and change in current indication.These indications are typically illustrated by channels 2 and 6 at the field station and channels 2 and 8 in the control office. When relay IV picks up during the first ofi period a circuit is closed for picking up relay P which extends from jumper I54 in its full line position, front contact I55 of relay IV back contacts I55 and I51 of relay 2V and 3V respectively, front contact I39 of relay VP Winding of relay P and front contact I33 of relay L0 to At this same time relay P is picked up over a circuit extending from front contact I5I of relay IV back contacts I52 and I53 of relays 2V and 3V respectively, front contact I43 of relay VP winding of relay P and front contact I34 of relay L0 to The shifting of contact I48 of relay P makes theenergization of relay P dependent on the No. 2 channel conductor, because the circuit through front contacts I48 and I4! of relays P and VP respectively lead to open contact I46 of relays IV With relays P and P picked up, the line is energized with a high current value as before because of closed front contacts I01 and IE8. When relay VP drops during the second on period the above described pick-up circuit for relay P is interrupted at front contact I43 and since the No. 6 channel conductor is now connected to the winding of relay P relay P is deenergized because code jumper I 58 is not connected to This results in the dropping of relay P during the second on period and with contacts In? and I08 out of correspondence, resistance IRS is inserted in the line circuit for changing the highcurrent energization to a low current energization.

This change in energization of the line circuit drops relay 2M but relay IM is maintained picked upfor executing the high current code by means of its stick circuit previously described, but it now extends through back contact 8| of relay VP, back contact 91 of relay 2V and front contact 88 of relay IV. This high current code is executed by energizing the No. 2 channel conductor from (13+) over the above described executing circuit, which now extends through back contact 15 of relay VP, back contact 98 of relay 3V and front contact 99 of relay IV, to the winding of relay 3PT for positioning the polar contact of this relay to the right.

The dropping of relay 2M in response to the change from a high to a low energization of the line circuit momentarily interrupts the stick circuit of relay CHI at contact 98, effecting the release of relay CHI and since its pick-up circuit is now open at back contact 86 of relay IV and front contact 81 of relay 2V, it remains down and when relay E is dropped to mark the end of the second on period the No. 6 channel conductor is energized over the above described circuit, which now extends from (B-) at back contact 9I of relay CHI and by Way of front contact 96 of relay IV to the winding of relay 4PT for positioning the polar contact of this relay to the left.

The above describes the transmission of four codes for effecting the station identification or registration of the typical station illustrated in Fig. 2. This code combination effects the picking up of station relay ST corresponding to the illustrated field station by means of a circuit Which extends from front contact 282 of relay IV, contacts 203, 204, and 285 of relays IPT, 2PT and 3PT respectively in their right hand positions, contact 206 of relay 4PT in its left hand position and winding of relay ST to The above four separate indication codes are transmitted during the first two on periods of the cycle, with the reception, registration and execution of these codes for station identification explained in detail. It will now be explained how the alternate codes, low current, no change and low current, change are transmitted in accordance with the indications to be transmitted from the identified field station. From this explanation it is believed that it will be obvious how these alternate codes are likewise transmitted in accordance with alternate positions of the code jumpers illustrated in Fig. 2 for identifying other stations in the control ofiice in accordance with these other code combinations.

The transmission of the above described code combinations for positioning the four pilot relays as described illustrates that sixteen different code combinations can be transmitted on two steps, fifteen of which can be used for station identification. This is because the four code jumpers illustrated in Fig. 2 can be arranged in sixteen different combinations, but the sixteenth code corresponds to a phantom indication code which must not be effective to register or identify a station in the control office because this code is inherently transmitted during a cycle for the transmission of controls alone, since during sucha cycle the line circuit will be energized during the first two on" periods with high current which is not changed in value. In brief, the code combination of high current, no change during the first on period and high current, no change during the second on period positions the four pilot relays to positions which do not select a station relay.

It has already been explained how relay CHI in the control office is conditioned by picking it up during the start period so that it may be dropped or not dropped during the first on period, as determined by the No. 6 indication being a change or no change respectively in the degree of energization of the line circuit. Relay CHI is conditioned in the first off period, the second off period and the third off period in preparation for being maintained picked up or dropped during the following on periods as determined by the 5, I and 8 indication codes transmitted. The pick-up circuit for relay CHI during the first off period extends through front contacts 84, 85 and 86 of relays SAP, VP and IV respectively and back contacts 81 and 88 of relays 2V and 3V respectively. The pick-up a tact of circuit for relay CHI in the second ofif, period is the samev except that it now extends through energizing lcircuit ifOI relayP is incomplete at open front contact ,1! 59 ofhrelay RD so that relay-P isynot u-pl-duringr thethird on period.

.Relay P risypicked fup during the second oil period because the Now! indication is no change inthe value of the energiZationofthe line circuit, that is'the'lineremains energized at a low value because relay P is not picked up" but relay P ispicked up duringthesecond off'period over aci'rc'uit extendingfrom fr'ont contact IQ! of r.elay*2V ,.back-contact l42' of relay 3V back contact M3 of relay'fVP winding of relay P and front contact l34-of relay L0 is 1 When relayVP -is picked up during the third on period this 'circuit'is interrupted but "relay P? remains energized'over a circuit extending through front contact I43 of -relay VP back contact llid-otrelay' 311 front contact I52 of relay 2V and front contact lfili of1'e1ay T to (-1-) Thus, since contacts M'iand H18 of relays P and P are out ofcorrespondence during the third on period, recurrences is low energization'of the line and the seventhcode is no change inenergization of the line.

Relay IM in the control office isnot picked up in response to the low degreeof energi'zation of the line circuit and this condition is executed by completing a circuit extending from (B-J, back contact 13 of relay IM, front contact 14 of relay E, front contact 15 ofrelay VP, front contact 29'! of relay 2V',"f ro nt' contact 208 ofrelay ST and winding ofrelay-f lIRto (CN). This positions the polarcon'tac't of relay IIR to the left. Polar conta'ctZElQ of relaylIR'jmay connect to an indicator lamp (not shown) for'indicating that relay RD is deenergized.

The no change indication-results in relay 2M remaining down so that the stick circuit of relay CHI 'is'not interrupted, with'theresult that the N011 indicationis executed over a circuit extending from (13+), 'front contactffil, of relay CHI. front contact safer relay FP, back Contact 930i relay E, back contact M of relaytV, front conrelay ZViffront coritac'tLZ ii] of relay ST an ne 21R. to ON), This position 's the polar'contact'of relay new the right, Polar contact 2J9 may control anj OS lamp (not shat/m fo iridicatirigiwhether or not track relay T1 is energiz d,

i l TheNolf l indication'is aflowdegree of line circult nergiza'tiqntrahsmitted in the same manneras Nol ii, becausefrcnt contactltl of relay LD is openfor deenergizing relay P when channel circuit 4 is closed at front contact I51 of relay 3V Relay P2 'is 'picked up during the third off period over a circuit extending through front contacts I 53am I43 or relays 3V and"VP respectively. When relay VP drops l during the fourth on period, relay P is from contact 1 12 of "relay 3V1 is open at front contact I62 ofrelay T 'This results inthe low changed to a high degreeiofyenergization' -because back contacts;:l01' .l08of relays P and P both close for short-circuitingresistance RS -This change from a'low to a high degree of line energization takes place during the fourth on period at-thetime'the VP relays drop, but before this happens relay lM'is conditioned by remaining down in response to the low degree of energization of the line circuit and when the VP relay in the ofiice picks up this condition of relay IM is executed by completing an energiz ing circuit for the N0. 4 channel circuit, which circuit now extends-through back-contact of relay VP, front contact 98 =of relay=3v and front contact 2 of. relay ST. The dropping of relay VP in thefourth on .tperiod disconnects the lower Winding of relay IM from "the'line circuit, since the circuit for energizing the line nowextends through backTcOntact -BG of 'relay VP and front contacts'3'l, l8 and saor relays IV, 2V and 3V respectively.

The change from a low to a high" degree of energization during thefourth o'n pe'riod picks up relay 2M in the control oflice and by means of contacts!!!) the'stic'k circuit for 'relayCHI is momentarily interrupted? which allows this re lay to release so that the chang'e of on indi'cation No. B'is executed ov'er a circuit extending from (B'), back contact 91 :ofrelay C-HLfront contact 92 of relay FP; back contact -93"of relay E, front contact 94- of relay 3V, front contact 2|2 of relay ST and winding ofrelay AIR/120 (CN). This positions polar contact 213 of relay 41R to the left which closes an energizing circuit for the OS lamp-by way of conductor 9ffo'r light I ing thislamp as anindication thattrack relay T at the station is" down; I f v From the above examples it is believed'obvious how additional indications maybe transmitted by providing additional stepping relays'in systems of larger size. The above examples illustrate how all eight combinations are transmitted, registered and receivedand 'it willbe understood that all these combinations may be used for station identification in syste'rn's of larger size.

Lock-out between stctioflsQ-It may happen that changes occur at more than onestation at the same time or in rapid successiomiiso that more than one station will have new' indications to transmit at the beginning of a cycle. In order to preventmorethan one 'st'ation actively associating itself with the communication circuits during thesame cycleIlock-out-means are providedateach station, effective to'sel'ect that station nearest the control office' having new indications to transrnit'; l Q I j When a change" occurs at the ifi'rst station, il-" lustrated inFigl 2, the normally 1 deenergized line is momentarily energizf'ed fr'omthe control ofiice line battery as previouslypointedout, When re-' lay NC in the control office dropsand when re lay SA picks up, the impulse of alternating current is applied to theline: for"efiedting the closure of the line circuit at the end station by relay SAP closing its frontfcontact 200'. The SA relay and the SAP relay at the illu'st-rated station will be picked up in sequence and in the interval between thepicking up of relay 'SA and the picking up of relay SAP the above described stick circuit for relay LO is open, be cause contacts and I3I of these tworelays are out of correspondence. 3 i I Rlelay L0 at'thefirst stationis maintained energized during this interva'b'from'the direct current provided--by the control ofiice' battery,

over the line circuit by Way of the A line conductor, front contact 224 of relay L back contact I28 of relay CH upper winding of relay L0 impedance 1M and back contact I22 of relay SAP to the B line conductor. At the station farther out the line having its LO relay picked up, the line circuit is not energized because the B line conductor is open at open front contact I22 of relay SAP open front contact I63 of relay CH and open back contact I64 of relay SA This deenergization of the line circuit extending beyond the first station'effects the dropping of the look-out relay, because the stick circuit for this relay is deenergized by the SA and SAP relays being out of correspondence and because the upper winding of the lookout relay is deenergized because the B line conductor is open.

After the SAP relays pick up, the continuity of the line circuit is again established but at this time it is too late for a lock-out relay at a more distant station to be picked up because of open back contact similar to contact I22 of relay SAP Since the picking up of the SA relay at a station farther out the line drops the associated lock-out relay after it has been picked up and since the line circuit is not energized after the picking up of the SA relay until the SAP relay is picked up, there is an interval of time during which the lock-out relays at the more distant stations cannot be energized through either winding. From the above it will be noted that the dead line for picking up a lock-out relay is the picking up of the associated SA relay and the consequent opening of its back contact, such as back contact I29 of relay SA As above mentioned, the line cannot be conditioned for indications at a station unless its lock-out relay is picked up and its contacts I33 and I34 are closed.

Although the lock-out feature has been explained with reference to the first station and other stationsof the system, it will be understood that similar conditions may exist between various combinations of stations, but it is believed that the explanation given is sufficient for an understanding of all such combinations, remembering that the nearest station to the control oflice with its lock-out relay picked up before the dead line is reached is a superior station and all others which may be picked up at this time are inferior stations, which will be dropped out when the system passes this dead line.

, Front contact I63 of relay CH which bridges back contact I64 of relay SA is for the purpose that control and indication cycles may each occur separately or simultaneously. The operations for control cycles alone and the operations for indication cycles alone have been described and it will now be pointed out how the system operates when controls and indications are transmitted during the same cycle.

The actuation of a starting buttonin the control oilice picks up its associated storing relay. During the time that the system is at rest and any time up to the end of the period marked off by the opening of back contact I4 of relay SAP, the CD relay associated with the actuated starting button can be picked up to mark the cycle as one for the transmission of controls. If a field station initiates the system after the SAP relay has been picked up, the control oilice cannot transmit controls during this cycle because of open backcontact I4, but it must wait until the beg'mning of the next cycle.

On the other hand, a lock-out relay at a field station may be picked up at the beginning of a cycle any time up to the picking up of the associated SA relay and the consequent opening of a back contact similar to I29 of relay SA of Fig. 2. After this contact is picked up the associated field station cannot actively associate itself with the communication circuits until the beginning of another cycle.

Therefore under the condition that the system is initiated by the picking up of a CD relay in the control ofiice and a lock relay at a field station at the beginning of a cycle, both controls and indications can be transmitted during this cycle. The polarity of each impulse applied to the line circuit is determined by the code jumper and lever connections selected by the energized CD relay. The identification or registration of a particular field station for the transmission of indications is determined by the particular lock-out relay which is picked up for effecting the transmission of indication codes as previously described. Since controls are transmitted outward from the control ofiice and since indications are transmitted inward to the control ofiice by the separate and independent conditioning of the twowire line circuit, these controls and indications may be simultaneously transmitted during the same cycle.

Since the transmission of outbound and inbound messages have been explained in detail for separate cycles of operation and since the line circuit is distinctively conditioned in a separate and distinctive manner for the transmission of both kinds of messages, it is not believed necessary to repeat the detailed description of these transmissions during a duplex cycle.

Modification It has been explained in connection with the registration of the high and low current impulses by relays IM and 2M of Fig. 1A, that these relays are so designed and adjusted that they will respond to high current energization but will not respond to low current energization, even though the low current flows through their pick-up windings. In other words, relays IM and 2M are of the marginal type.

The arrangement disclosed in the Fig. 3 modification provides a means for using one or more message relays for receiving the transmitted over the line circuit, which relays are not of the marginal type. This is accomplished by determining the amount of grid bias applied to a vacuum tube, having one or more relays connected in its plate circuit, as illustrated by relay M of Fig. 3.

The arrangement is shown in abbreviated form, with the line circuit arrangement of the other figures illustrated somewhat in detail to indicate that this modified circuit may be applied to the previously described transmitting arrangement. The indication transmitting contact at the field station is illustrated as contact 300, operated by impulse relay P for short-circuiting resistance indications RS to provide a high degree gization.

, The PC, NC, SAP and SA relay contacts are of line circuit ener illustrated, with these relays having the same reference characters as corresponding relays in the Fig. 1A modification, but with the exponent 3 added. It willbe understood that the opera tion for the transmission of controls and for the transmission of indications is the same as previously described. It will now be explained how theindications are received in the control oflice.

It will be, obvious that a contact may be provided on start relay STR. and on code determin ing relay CD for controlling the energization of the tube circuits when the system is initiated. This provides heating current for the heater element of the tube and a comparatively high pocordance with the operations of relays PC and NC is applied to the terminal of the bias resistor which connects tothe grid.

Assuming that a control impulse is applied to the A line conductor, current flows from the terminal of battery L33, through relays F F and F .(at. the end station or at other stations connected to the line circuit), returning to the f terminal of battery LB by way of the B line conductor and bias resistor BB The resistance values of the line relays in the line circuit and the line circuit itself (with resistance RS shortcircuited) are so related that under this condition the grid of the tube is made sufiiciently positive to cause its plate circuit to conduct. Since relay M is included in the plate circuit and since the tube will pass current in only one direction, pulsating current is applied to the winding of this relay for picking it up to register a first indication condition.

When a control impulse is applied to the line circuit, the connection to the line is reversed beyond bias resistor BB with respect to the line battery, so that the same polarity occurs at the terminals of the bias resistor BB as before.

The other indication condition is transmitted when relay P is down to insert resistance RS in the line circuit. The inclusion of this resistance in series with resistance BB lowers the positive potential applied to the grid of the tube beyond the cut-off point so that the tube. is rendered nonconducting. Therefore relay M does not receive any current under this condition and with this relay deenergize-d the second indication condition is registered.

The reason that the grid or detecting circuit of the vacuum tube thus discriminates between the potential existing across the terminals of resistance BB under the above described conditions may be stated in this way. By decreasing the value of the resistance in the line circuit (by short-circuiting resistance RS more current flows from battery LB through resistance 3R so that the IR drop through resistance BB becomes greater, with that terminal of the resistance remote from the terminal of battery Ll? becoming more positive in potential. Since the grid is connected at this point, its potential becomes more positive with respect to the cathode, which is connected to the terminal of the battery.

It will be noted that this arrangement differs With this resistor located at materially from the arrangement disclosed in Fig. 1A, in which the marginal relay detects, by picking up or not picking up, the exclusion or inclusion of the resistance at. the field station. In other words, the arrangement disclosed in Fig. 3 is a voltage operated device in which a difference in potential brought about by the inclusion of a resistance in the line circuit at the field station is used for controlling the circuit in which the message relay is included, so that this circuit receives current or does not receive current. Therefore, message relay M does not need to be marginally adjusted and designed with respect to the circuit in' which it operates, but it may be so designed that it responds to current flow of any material value.

Although one specific embodiment and one modification of the invention have. been shown, it is to be understood that various rearrangements may be made and still come within the scope of the invention. n

Having thus described a centralized traffic com trolling system as one specific embodiment of the present invention, itis desired to be understood that this form is selected to facilitate in the disclosure rather than to. limit the number of forms which the invention may assume and it is further to be understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice without in any manner departing from means for p-ositioning said relays in correspond ing and non-corresponding positions, means including said relays in corresponding positions for transmitting a first code over said line circuit comprising an impulse of current of comparatively high value, and means including said relays in non-corresponding positions for transmitting a second code over said line circuit comprising an impulse of current of comparatively low value.

2. In a code transmitter, a line circuit over which codes are transmitted, a pair of relays, means for positioning said relays in corresponding and non-corresponding positions, means including said relays in corresponding positions for transmitting a first code over said line circuit comprising an impulse of current of comparatively high value, means including said relays in non-corresponding positions for transmitting a second code over said line circuit comprising an impulse of current of comparatively low value, means for changing the position of a first one of said relays during the transmission of either said first or said second code, and means responsive to said change in position of said first relay for transmitting a third code over said line circuit comprising a change in the degree of energization of said line circuit.

3. In an impulse transmitting system, a loop impulse transmitting circuit, means at one end of said loop circuit for generating and transmitting time spaced impulses of current over said circuit, code transmitting means at the other end .of said loop circuit, a relay controlled by said code transmitting means for by the position assumed by its contact determining the initial high or low strength of each of said impulses to form codes, and a second relay controlled by said code transmitting means for when operated to either change said current strength from a high to a low or from a low to a high current strength during subsequent portions of said impulses to form additional codes.

4. A selector system for transmitting distinctive codes over a line circuit from a station to an ofiice comprising, a line circuit connecting said ofiice and said station, means at said ofiice for intermittently energizing said line circuit with a plurality of impulses of normally high current value, means including a first relay at said station for making the first part of each of said impulses of abnormally low current value or leave it at said normally high current value to form a first code, means including a second relay at said station for either changing or leaving unchanged the value of the current during the second part of each of said impulses to form a second code, and code responsive means in said ofiice selectively responsive to said first and said second codes.

5. In a remote control system of the selector type, the combination with a control office and a field station, of a line circuit connecting said office with said station, impulsing means at said office for energizing said line circuit with a plurality of impulses to define a code period, means including a first relay at said station for establishing a current strength of high or low value for each impulse during the first part of each of said impulses to form a code, and means including a second relay at said station for during a second part of each impulse changing said high current to a low current, a low current to a high current or leave unchanged the current strength of said impulses to form a second code.

6. In a remote control system of the character described; the combination with a control ofiice and a field station; a line circuit connecting said oflice and said station; impulsing means at said office for energizing said line circuit with a plurality of impulses to define a code sending period; means including a first relay at said station for establishing a current strength of high or low value for each impulse during the first part of such impulse to constitute a plurality of impulses of a code transmitted within said code period; and means including a second relay at said station for during. the second part of each impulse changing such impulse from a high or a low value as determined by said first relay to a low or a high value respectively, or for leaving the value of said impulse asdetermined by said first relay to form a second code.

'7. In a remote control system, a line circuit having a plurality of series of time spaced impulses of distinctive strength impressed thereon, a step-by-step mechanism operable through a separate cycle for each of said series, means controlled by said mechanism for selecting two local channel circuits for each step, means for causing said mechanism to take one step for each time space between successive impulses of a series, means including a first relay for at times deter mining the strength of said impulses during their impression on said line circuit, means including a second relay for at times thereafter changing the strength of the current as determined by the first relay during each of said impulses, means for distinctively energizing one of said channel circuits in accordance with the strength of the impulse impressed in said line circuit for that step, and means for distinctively energizing the other of said channel circuits in accordance with whether there has been a change or no change in the strength of the impulse during that impulse for that step.

. WINFRED T. POWELL. 

